Oil permeable paper laminated cylinder and the like



Dec. 27, 1966 c. F. FOSTER ETAL 3,294,123

OIL PERMEABLE PAPER LAMINATED CYLINDER AND THE LIKE Filed Sept. 18, 1963 United States Patent 3,294,123 OIL PERMEABLE PAPER LAMINATED CYLINDER AND THE LIKE Charles F. Foster, Maple Glen, Pa., and Frank S. Nichols,

Pittsfield, and Eugene K. Steele, Dalton, Mesa, as-

signors to General Electric Company, a corporation of New York Filed Sept. 13, 1963, Ser. No. 309,765 2 Claims. (Cl. 138-144) This invention relates to laminated paper structures and the method of making such structures and, more particularly, to an oil permeable paper laminated cylinder and the like.

In the electrical art, and in particular electromagnetic induction apparatus, it is common to utilize cylinders of insulating material, such as paper, for coil winding forms and also as insulation between the legs of electromagnetic cores and coils wound on such legs. As is well known, the core and coil structures are in many instances enclosed in a tank with a dielectric fluid within the tank completely covering the core and coil structure. An example of such dielectric fluid is the well-known electrical grade mineral oil. In these apparatuses it is necessary that the insulated cylinder be either permeable to the flow of the fluid in which it is immersed or be completely impermeable and free from air pockets trapped in the insulating cylinder. As is known, air pockets in the cylinders degrade its insulating properties and lower the voltage rating of the device. In view of the difficulties encountered in the manufacture of cylinders free from air pockets, the permeable type of insulating cylinder is generally considered more desirable. In general, prior to the introduction of a dielectric fluid into a tank containing a core and coil unit, heat and vacuum are applied to remove moisture and airfrom the tank and the core and coil unit therein. During the evacuation air and moisture are extracted from the insulating materials thereby allowing the dielectric fluid to penetrate the materials and improve their insulating properties.

The insulating cylinders utilized are generally comprised of a number of layers of kraft paper bonded together with adhesive material to form a unitary structure. These adhesive materials normally penetrate the paper and when cured form a solid, hard mass of paper in resin. In general, the adhesives solidify into an impervious mass and as a result complete coverage of the paper with such adhesive was avoided. The adhesive is normally applied to the paper in strips or in some pattern such that many small areas free from adhesive are provided within the paper lamination. By means of these many small areas the laminated cylinder is not bonded together at these points. The areas which are free from adhesive lend porosity to the cylinder allowing the dielectric fluid to pass freely through the laminated cylinder, since the paper from which it is made is generally relatively permeable to the dielectric fluid. However, the cylinders wherein the layers of paper are not completely bonded together do not possess the high mechanical strength generally considered necessary and are susceptible to delamination during treatment due to these unbonded portions. As is well known, in the production of these cylinders it is necessary to employ a relatively expensive method since the quantity of the adhesive deposited and the location of the adhesive had to be controlled in order to obtain the desired pattern. Of course, this method also provides for increased use of skilled labor in order to obtain the desired permeable laminated structure. For this reason, there has been a demand for laminated cylinders which can be inexpensively made, which are mechanically strong and yet which will be permeable to dielectric fluids to obtain optimum electric characteristics of the insulating cylinder.

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A very desirable approach is to completely cover the paper with adhesive. With this approach, little machinery is required because it is only necessary to apply the adhesive to a sheet of paper as it is being rolled into a tube. The uniform spreading of the adhesive is obtained by the paper in the region where it merges with the roll since the adhesive is uniformly spread into a thin layer by the contact of the paper with the roll. Of course, the mechanical strength of the cylinder will be uniform throughout the entire structure. It has recently been discovered that an adhesive of a suspension of a polymer in a nonsolvent medium can be applied to paper in a uniform layer to produce a laminated structure of uniform mechanical strength and rigidity where the paper is substantially bonded together to form a strong laminated structure, and in which the wall is permeable to the free flow therethrough of the dielectric fluid normally used in electromagnetic induction devices for cooling and insulating purposes.

It is, therefore, one object of this invention to provide a paper laminated cylinder that is permeable to oil.

A further object of this invention is to provide a paper laminated cylinder in which paper is bonded together by an adhesive which allows oil to penetrate the walls of the cylinder.

Briefly, in one form this invention relates to a paper laminated cylinder wherein the paper is bonded together by an emulsion or suspension of polymer particles applied in a nonsolvent liquid medium, which adhesive bonds the paper into a strong laminated cylinder while permitting penetration of a dielectric fluid through the walls of the cylinder.

The invention which is desired to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner of carrying it out, as well as the manner in which its various objects and advantages are obtained, will be better understood from the following detailed description of a preferred embodiment thereof, especially when considered in the light of the accompanying drawing, in which:

FIGURE 1 is a schematic view of one method of making a paper laminated cylinder according to this invention; and

FIGURE 2 is a sectional view of a paper laminated cylinder incorporating this invention.

Referring now to the drawing, FIG. 1 shows one method of making an oil permeable paper laminated cylinder according to this invention. As is shown in FIG. 1, a mandrel 10 is utilized to form the paper into a paper cylinder, which is generally indicated at 12. A roll of paper 14, which in the art is generally a low water finished kraft paper, is mounted on a payout reel 16 in the manner shown, and the paper, indicated at 18, is directed from the reel 16 to the mandrel 10 through a winding roll 20. In order to firmly bond the various layers making up the cylinder 12 an adhesive, indicated at 22, is maintained in a tank 24 and is fed by means of a tube 26 on to the paper 18 forming a small pool 28 at the nip of the roll between the paper 18 and the roller 20. The adhesive 22 is a suspension of polymer particles in a nonsolvent liquid medium and is poured by means of tube 26 directly on to the sheet 18, in the manner shown. In general, the method is carried out at room temperature and there is no set winding speed for winding the sheet 18 into the laminated paper cylinder 12. The only limiting factor that has been found is winding at a speed in which the pool 28 can be maintained so as to provided a thorough coating of the sheet 18 with the polymer suspension 22 prior to wrapping on the mandrel After the cylinder has been wound on the mandrel to the desired thickness the mandrel with the cylinder thereon is placed in an oven and the resin is cured. The cure cycle is not critical and satisfactory cylinders can be produced even though the cure cycle is varied over wide limits. A heat treating cycle of two hours at 100 C. followed by four hours at 150 C. has been found to give consistently good results. After the cylinder has been cured it may be removed from the mandrel and used in electromagnetic induction apparatus, in the well known manner.

Referring now to FIG. 2 of the drawing, there is shown a sectional view of the cylinder 12 after curing with the mandrel removed. As shown, cylinder 12 comprises a number of layers of paper, only two being shown, the inner layer 30 and the outer layer 32; the layers 30 and 32 being firmly bonded together by the dried, cured resin indicated at 34. Of course, it will be understood that any number of layers may be wrapped to form the cylinder 12 and each layer will be adhered to the adjacent layer by the cured resin 34, in the manner shown in FIG. 2.

The material which is applied to the sheet 18 to obtain the desired resin coating may be of any known types of composition which consist essentially of a suspension of extremely small particles of solid polymers in a non solvent liquid such as Water; the particle size being typically about 1 to 500 microns. These materials are normally made by the emulsion polymerization of one or more liquid polymerizable monomers, the emulsification of the original monomers producing a very small size particle of polymer. The monomers used may be difunctional giving rise to thermoplastic polymers, common examples which are used commercially being vinyl acetate and various acrylic esters. Alternatively, the monomers may be polyfunctional provided that two of the functional sites may be preferentially reacted to produce minute particles of a thermoplastic polymer which by further reaction can convert to a thermoset polymer. A number of types of adhesives which may be used in practicing this invention are specifically set forth in application Serial No. 856,434, filed December 1, 1959 for Electrical Coils and Method of Making the Same, in the names of Frank S. Nichols and Eugene K. Steele, two of the inventors herein; said application being assigned to the same a"- signee as this application. A specific example of the adhesive which may be used and which is set forth in the above-mentioned application Serial No. 856,434 is as follows:

EXAMPLE I Ingredients Parts by wt.

Polymerizable monomers:

Acrylonitrile 63.0

Butyl acrylate 32.0

Methacrylic acid 3.0

Glycidyl methacrylate 2.0 Polymerization initiator:

Sodium bisulfite 0.1

Potassium persulfate 0.3 Dispersing agent:

Sodium lauryl sulfate 0.5 Telogen:

Dodecyl mercaptan 0.5 Water 200.0

In all cases, the product which is utilized in practicing the invention is a stable suspension of minute fusible particles of a polymer in a nonsolvent medium, preferably water. In use the suspension is coated onto the paper in the manner, for example, shown in FIG. 1 of the drawing, and as the suspension loses water by drying it becomes unstable and the polymer particles are deposited on the paper 18. The particles may then subsequently be baked to fuse them together, or in the case of thermosetting resins, to complete the second stage of polymerization and cured. If desired, small amounts of solvent for the polymer may be added to the suspension to facilitate fusion of the polymer particles without adversely affecting the operation of the adhesive for purposes of the invention.

While it is apparent that improved results are obtained by the present invention since the dielectric fluid of the electrical apparatus readily permeates the laminated cylinder made according to this invention, the reason for the improved permeability is not fully understood. It is believed that during the curing cycle the resin crazes while still maintaining its mechanical strength and that it is the unique property of crazing of the resin Which renders this structure fluid permeable. In general, an extremely large number of small cracks develop in the adhesive, resinous material during the curing, converting it into a porous medium. These cracks occur at random, are discontinuous and penetrate the layers of resinous material. However, for whatever reason, it is known that the use of a fused particulate resinous material as an adhesive provides a fiuid permeable structure. Thus considerable porosity of the structure is obtained by use of the particulate adhesive material providing an oil permeable paper laminated cylinder in accordance with the objects of this invention.

While the above method of making an oil permeable paper laminated cylinder is considered preferred, there are other possible methods in carrying out the invention. For example, paper pro-coated with resin particles could be wound in dry form and the resin cured to obtain a bonded tube. In this case the paper would first be coated with the resinous emulsion, dried to remove the water and then placed in storage until needed. It would also be possible to add the polymer emulsion into the beater at the mill to obtain the desired oil permeable adhesive on the paper. Another possible variation would be to spray a water emulsion on to the paper as such paper iS being wrapped into the cylinder.

While the present invention has been described with reference to the particular preferred embodiment it will be obvious that many modifications may be made by those skilled in the art without departing from the scope of the invention. Therefore, it will be understood that it is intended to cover equivalent variations which come within the spirit and scope of the invention defined within the appended claims.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A laminated cylinder comprising a plurality of layers of paper, each layer being bonded to an adjacent layer by a fluid permeable adhesive coating applied in the form of a suspension of polymer particles in a non-solvent medium, said fluid permeable adhesive crazing during curing which bonds said adjacent layers together, said crazed adhesive coating having cracks extending completely through said adhesive coating making said adhesive coating iluid permeable.

2. An oil permeable paper laminated cylinder comprising a plurality of layers of fluid permeable paper bonded together by a fluid permeable adhesive coating applied from a suspension of polymer particles in a non-solvent medium which crazes on curing, said crazed adhesive having cracks extending completely through said adhesive and cooperating with the fluid permeable paper to render the cylinder fluid permeable.

References Cited by the Examiner UNITED STATES PATENTS 2,246,159 6/1941 Work et al. 33694 2,707,155 4/1955 Fenwick 33694 X 3,203,823 8/1965 Grimes 174-17 X FOREIGN PATENTS 186,857 8/1936 Switzerland.

SAMUEL ROTHBERG, Primary Examiner.

LAVERNE D. GEIGER, C. L. HOUCK,

Assistant Examiners. 

1. A LAMINATED CYLINDER COMPRISING A PLURALITY OF LAYERS OF PAPER, EACH LAYER BEDING BONDED TO AN ADJACENT LAYER BY OF FLUID PERMEABLE ADHESIVE COATING APPLIED IN THE FORM OF A SUSPENSION OF POLYMER PARTICLES IN A NON-SOLVENT MEDIUM, SAD FLUID PERMEABLE ADHESIVE CRAZING DURING CURING WHICH BONDS SAID ADJACENT LAYERS TOGETHER, SAID CRAZED ADHESIVE COATING HAVING CRRACKS EXTENDING COMPLETELY THROUGH SAID ADHESIVE COATING MAKING SAID ADHESIVE COATING FLUID PERMEABLE. 